Buck converters are converter circuits for converting a DC input voltage into a DC output voltage. As shown in DE 102 43 885, a known Buck converter topology has at its input a half bridge with a first switching element and a second switching element. An inductance is connected between the node which is between the switching elements, and a load. The switching elements are in each case alternately driven, for example by means of pulse-width control. Such Buck converters are used especially for the voltage supply of microprocessors, e.g. in PCs.
In this context, multi-phase Buck converters are also used as described in U.S. Pat. No. 6,839,252. In this arrangement, the Buck converters contain a number of half bridges of in each case two power transistors. The power transistors are switched on and off by different phases and thus at different times. The current is thus distributed over a number of half bridges in order not to overload the power transistors located in the half bridges. In addition, the ripple of the output voltage is reduced since the switching-on and switching-off processes are distributed over a number of phases. However, providing the large number of power transistors means increased space and circuit expenditure.